Crystal structures of human soluble adenylyl cyclase reveal mechanisms of catalysis and of its activation through bicarbonate.

TitleCrystal structures of human soluble adenylyl cyclase reveal mechanisms of catalysis and of its activation through bicarbonate.
Publication TypeJournal Article
Year of Publication2014
AuthorsKleinboelting S, Diaz A, Moniot S, van den Heuvel J, Weyand M, Levin LR, Buck J, Steegborn C
JournalProc Natl Acad Sci U S A
Volume111
Issue10
Pagination3727-32
Date Published2014 Mar 11
ISSN1091-6490
KeywordsAdenylyl Cyclases, Catalysis, Cloning, Molecular, Crystallization, Enzyme Activation, Humans, Models, Molecular, Protein Binding, Protein Conformation, Signal Transduction, Sodium Bicarbonate
Abstract

cAMP is an evolutionary conserved, prototypic second messenger regulating numerous cellular functions. In mammals, cAMP is synthesized by one of 10 homologous adenylyl cyclases (ACs): nine transmembrane enzymes and one soluble AC (sAC). Among these, only sAC is directly activated by bicarbonate (HCO3(-)); it thereby serves as a cellular sensor for HCO3(-), carbon dioxide (CO2), and pH in physiological functions, such as sperm activation, aqueous humor formation, and metabolic regulation. Here, we describe crystal structures of human sAC catalytic domains in the apo state and in complex with substrate analog, products, and regulators. The activator HCO3(-) binds adjacent to Arg176, which acts as a switch that enables formation of the catalytic cation sites. An anionic inhibitor, 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid, inhibits sAC through binding to the active site entrance, which blocks HCO3(-) activation through steric hindrance and trapping of the Arg176 side chain. Finally, product complexes reveal small, local rearrangements that facilitate catalysis. Our results provide a molecular mechanism for sAC catalysis and cellular HCO3(-) sensing and a basis for targeting this system with drugs.

DOI10.1073/pnas.1322778111
Alternate JournalProc. Natl. Acad. Sci. U.S.A.
PubMed ID24567411
PubMed Central IDPMC3956179
Grant ListR01 GM062328 / GM / NIGMS NIH HHS / United States
R01 HD059913 / HD / NICHD NIH HHS / United States
GM62328 / GM / NIGMS NIH HHS / United States
HD59913 / HD / NICHD NIH HHS / United States